Absorbable copolymers of randomly polymerized glycolide and caprolactone are described. Processes for making the copolymers and surgical articles made totally or in part from such copolymers, including sutures, are also described.
Bioabsorbable surgical devices made from copolymers derived from glycolide and epsilon-caprolactone are known in the art. Such bioabsorbable surgical devices include surgical sutures.
A desirable characteristic of a bioabsorbable suture is its ability to exhibit and maintain desired tensile properties for a predetermined time period followed by rapid absorption of the suture mass (hereinafter xe2x80x9cmass lossxe2x80x9d.)
Synthetic absorbable sutures are known in the art. Absorbable multifilament sutures such as DEXON sutures (made from glycolide homopolymer and commercially available from Davis and Geck, Danbury, Conn.), VICRYL sutures (made from a copolymer of glycolide and lactide and commercially available from Ethicon, Inc., Sommerville, N.J.), and POLYSORB sutures (also made from a copolymer of glycolide and lactide and commercially available from United States Surgical Corporation, Norwalk, Conn.) are known in the industry as short term absorbable sutures. The classification short term absorbable sutures generally refers to surgical sutures which retain at least about 20 percent of their original strength at three weeks after implantation, with the suture mass being essentially absorbed in the body within about 60 to 90 days post implantation.
Long term absorbable sutures are generally classified as sutures capable of retaining at least about 20 percent of their original strength for six or more weeks after implantation, with the suture mass being essentially absorbed in the body within about 180 days post implantation. For example, PDS II sutures (commercially available from Ethicon, Inc., Sommerville, N.J.), are synthetic absorbable monofilament sutures that reportedly retain at least about 20 to 30 percent of its original strength six weeks after implantation. However, PDS II reportedly exhibits minimal mass loss until 90 days after implantation with the suture mass being essentially absorbed in the body about 180 days after implantation. MAXON suture (commercially available from Davis and Geck, Danbury, Conn.) is another absorbable synthetic monofilament that reportedly generally fits this absorption profile.
Most recently, United States Surgical Corporation has introduced BIOSYN monofilament sutures which exhibit good flexibility, handling characteristics, knot strength and absorption characteristics similar to those of presently available short term absorbable multifilament sutures.
Another attempt to provide an acceptable synthetic absorbable monofilament sutures resulted in MONOCRYL, a suture fabricated from an absorbable block copolymer containg glycolide and caprolactone, commercially available from Ethicon, Inc.
However, no synthetic absorbable monofilament sutures exist today which approximate the strength retention, mass loss, and modulus of sutures commonly referred to in the art as xe2x80x9ccatgutxe2x80x9d or xe2x80x9cgutxe2x80x9d sutures. It is well known in the art that the term gut suture refers to a collagen based suture of any type or origin often fabricated from the mammalian intestines, such as the serosal layer of bovine intestines or the submucosal fibrous layer of layer sheep intestines. Gut sutures exhibit the unique combination of two week strength retention and about 75 day mass loss while maintaining acceptable modulus and tensile strength; and thus are still widely used in gynecological surgery.
It would be advantageous to provide a synthetic absorbable suture which exhibits physical properties similar to the gut suture.
U.S. Pat. No. 4,700,704 to Jamiolkowski does teach that sutures can be fabricated from random copolymers of glycolide and epsilon-caprolactone, and more specifically from random copolymers containing from 20 to 35 weight percent epsilon-caprolactone and from 65 to 80 weight percent glycolide. Moreover, Jamiolkowski reports that sutures fabricated from glycolide/epsilon-caprolactone copolymers containing over 35% caprolactone under are not orientable to a dimensionally stable fiber. Jamiolkowski further reports that some sutures fabricated from glycolide/epsilon-caprolactone copolymers containing 15% caprolactone are also not orientable to a dimensionally stable fiber. Furhermore, Jamiolkowski also reports the undesirable combination of low modulus and low tensile strength for the glycolide/epsilon-caprolactone copolymers which he was able to fabricate into sutures.
Therefore, it would be unexpected that sutures made from random copolymer of glycolide and epsilon-caprolactone would provide the strength retention and mass loss characteristics approximating those of gut sutures while maintaining an acceptable modulus and tensile strength.
It has now surprisingly been found that absorbable surgical articles formed from a random copolymer of glycolide and caprolactone exhibit strength retention, mass loss and modulus similar to that of gut sutures. Preferably, the copolymers used in forming surgical articles include between about 25 and about 32 weight percent of hydroxy caproic acid ester units and between about 75 and 68 weight percent of glycolic acid ester units.
In particularly useful embodiments, the random copolymers can be spun into fibers. The fibers can be advantageously fabricated into either monofilament or multifilament sutures having physical properties similar to those of gut sutures.
In addition, a process of making such synthetic absorbable monofilament sutures from the above described caprolactone/glycolide random copolymers has been found. The process, for a given size suture, comprises the operations of extruding the random caprolactone/glycolide copolymer at an extrusion temperature of from about 70xc2x0 C. to about 215xc2x0 C. to provide a monofilament fiber, passing the solidified monofilament through water (or other suitable liquid medium) quench bath at a temperature of from about 15xc2x0 C. to about 25xc2x0 C. or through in air (or other suitable gaseous medium) at from about 15xc2x0 C. to about 25xc2x0 C., stretching the monofilament through a series air ovens at an overall stretch ratio of from about 7:1 to about 14:1 to provide a stretched monofilament. In a particularly useful embodiment, the monofilament is stretched through three air ovens by four godet stations. The first air oven is maintained at ambient temperature, whereas the second air oven is heated to a temperature above the crystalization temperature of the glycolide/epsilon caprolactone copolymer at about 80xc2x0 C. to about 110xc2x0 C., and the third air oven is set at about 85xc2x0 C. to about 120xc2x0 C. The draw ratio between the first and second godet station ranges between about 5:1 to about 8:1. The draw ratio between the second and third godet station ranges between about 1.3:1 to about 1.8:1. The draw ratio between the third and fourth godet station ranges between about 1.04:1 to about 1.06:1. The suture then may be annealed with or without relaxation at a temperature of from about 80xc2x0 C. to about 120xc2x0 C. to provide the finished suture.